Ferrous metal structures are commonplace in many industrial settings such as power producing plants, windmills, factories or shipyards, storage structures, buildings and bridges. These structures are often irregular and will be described as unstructured environments. Depending on the nature of the structure, periodic inspection and maintenance is required, often through standard maintenance practices. In many instances, regular inspections of these structures are required by regulatory agencies such as EPA, for example if the structure is used to hold a chemical liquid. In order to perform the examination, manual inspection is generally performed using tools consisting of a nondestructive examination technology such as ultrasonic inspection. Nondestructive examination tools place requirements on the overall inspection process, such as a certain level of surface preparation, applying liquids on the surface, placing the nondestructive examination tool transducer at a specific position and orientation relative to the surface, and manipulation of the transducer based on feedback from the nondestructive examination tool output.
Because of these requirements, inspection using nondestructive examination tools is usually done manually by a trained technician. In unstructured environments, this requires the technician to be placed directly in the proximity of any location to be inspected. This potentially poses a safety hazard to the human operator. It also increases the cost of such inspection due to the need for the trained operator, safety and support systems.
The use of a mobile-platform, climbing vehicle capable of navigating part or all of a structure while carrying and manipulating inspection equipment represents a method to make the inspection process safer, cheaper and more reliable. A number of mobile climbing systems designed for inspection or related activities are demonstrated in the prior art. The prior art of climbing vehicles inspection tasks typically generate adhering forces through one of two methods, magnetic forces or vacuum (pressure) forces. The means to integrate these into a moving platform are more diverse with the general methods summarized here.
Wheeled or endless track devices making use of vacuum pressure include the following. U.S. Pat. Nos. 7,520,356 and 7,076,335 show vehicles that use wheels or endless tracks with the vacuum seal devices attached to the frame of the vehicle and slide over the climbing surface. U.S. Pat. No. 7,520,356 includes the ability to connect these vehicles in a modular fashion with the ability to transition between wall surfaces. US patent application no. US 2005/0072612 A1 shows a combination of wheel and endless-track drive that simultaneously provides driving forces and a perimeter seal for suction adhering to vertical surfaces.
There are also examples of legged-type vehicles making use of vacuum pressure, for example, U.S. Pat. No. 5,551,525 demonstrates a legged-type climbing robot with vacuum cups for adhering members.
Wheeled or endless track devices that make use of magnetic forces include the following. U.S. Pat. Nos. 3,764,777, 5,853,655, 6,627,004, 5,809,099 and Fisher, Tache and Siegwart (2008) show variations of climbing vehicles with magnetic wheels whose axes are fixed to the vehicle chassis. U.S. Pat. No. 7,309,464 shows a magnetic wheel carriage with wheel axes supported on the vehicle frame but given an additional degree of freedom such that the magnetic wheels are steerable.
US Patent application publication US 2010/0176106 A1 shows a magnetic wheel carriage with magnetic wheels that rotate about axes that are able to change orientation relative to the vehicle frame. The additional mobility in the wheel axes allows a larger number of wheels to make contact with a climbing surface when operating on non-flat or non-uniform climbing surfaces.
U.S. Pat. No. 5,435,405 shows an example of a type of climbing carriage or vehicle that contains magnets or similar adhering members attached to endless tracks, with multiple magnets attaching to the climbing surface at any given time. However, these systems tend to either place the magnets on a track without a track guide or mechanism between the end wheels (for example U.S. Pat. No. 5,884,642 or Shen and Shen, 2005) and rely on tension in the track to transfer climbing forces to the adhering members, or on a track with a rigid track guide limiting the ability to conform to a non-uniform climbing surfaces (for example U.S. Pat. No. 5,487,440, Kim et al., 2008) or a guide that has some flexibility but for purposes of pushing in a single direction on the track to make contact with the climbing surface (for example U.S. Pat. No. 4,789,037). When climbing the loads required to maintain equilibrium are transferred to the adhering members according to the relative compliance of the carriage frame and endless track system and in general will be localized to a small number of the adhering members causing degradation in holding power.
The existing prior art demonstrates differing technical approaches for climbing or traversing inclined or inverted surfaces while carrying and positioning a payload such as an inspection transducer. To be robust, the systems must be able to accommodate variations or irregularities in the climbing surface, and maintain an optimal use of the adhering forces required to adhere and maintain equilibrium on the climbing surface and to have a large payload to weight ratio. The payload will include the inspection transducer and in many cases tooling to clean or otherwise prepare the surface for inspection. In this regard, the technology demonstrated in the prior art suffers from a few distinct drawbacks which are discussed here.
The systems that employ magnetic wheels with axes rigidly attached to the vehicle chassis, or that attach magnets directly to the vehicle chassis lack the ability to accommodate variations in the climbing surface, and will lose adhering force and traction when traveling over surfaces that have a certain degree of geometric irregularity. The vehicle systems that use magnetic wheels on moving axes do not demonstrate a means to distribute climbing loads among the wheels and therefore can cause the adhering forces to be localized in one or a few of the magnetic wheels. The systems that employ endless tracks with magnets or other adhering members attached, and the endless track passing through a rigid guide attached to the vehicle frame lack the ability to accommodate variations in the climbing surface, and will lose adhering force and traction when traveling over surfaces that have a certain degree of geometric irregularity. The systems that employ endless tracks with magnets or other adhering members attached, and the endless track is not connected to the vehicle frame through some type of guide will cause the adhering forces to be localized to the exterior magnets on the contact portion of the endless track. Systems that employ endless-tracks also can cause undesirable motions in the inspection transducer that can reduce the efficiency of inspection. Systems that employ vacuum pressure forces for adhering rely on compliant or flexible portions of the vacuum cup (U.S. Pat. Nos. 7,520,356 and 7,076,335) or compliant surface of the endless track itself (US 2005/0072612 A1) to accommodate surface irregularities and enforce the perimeter seal required to maintain the vacuum forces However, the degree of surface irregularity permitted is limited by the availability and durability of the compliant materials.
There are two methods demonstrated in the prior art that attempt to simultaneously accommodate surface forces and distribute climbing forces. Xu and Ma (2002) shows an endless-track type climbing vehicle with type of climbing vehicle with magnets called magnetic suckers. A load distribution mechanism is presented as a three link member connected to the vehicle body with a single spring. The article does not show how the endless track would connect with the load scatter mechanism or how forces are transferred from the track to the mechanism. Further, as presented, the load scatter mechanism localizes moment-balance forces to the leading portion of the load scatter mechanism and similarly the leading edge of the endless track. Canfield and Beard (US Patent application 2010) show a compliant-beam suspension mechanism for an endless track type climbing vehicle that relies on elastic compliance of a beam to match surface irregularities and distribute loads. In practice, engineering materials are not readily available that can accommodate large strains required by this for surfaces with significant variation.